This application claims the priority of Japanese Patent Application No. 10-96785 filed on Mar. 25, 1998 and Nos. 10-103792 and 10-103793 filed on Mar. 30, 1998 which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electronic-endoscope light source unit, particularly to a structure for adjusting the luminous energy of video signals for reading every pixel by an electronic endoscope for reading the signal of every pixel accumulated in an image pickup device by setting a shading period.
2. Description of the Prior Art
In the case of an electronic endoscope system, a video signal is formed by reading electric charges accumulated by a photoelectric conversion device in pixels by a CCD (Charge Coupled Device) serving as a solid-state image pickup device. Moreover, in the case of a simultaneous-type electronic endoscope system, color filters are arranged on the CCD in pixels and thereby, a color image can be obtained.
FIG. 14 shows how the color filters are arranged. As shown in FIG. 14, Mg (magenta) and Cy (cyanogen) pixels are arranged on even lines of the image pickup face of a CCD 1 in pixels and G (green) and Ye (yellow) pixels are arranged on odd lines of it in pixels. The CCD 1 makes it possible to obtain accumulated electric charges (pixel signals) in pixels through these color filters.
Moreover, according to a conventional mixing read mode, accumulated electric charges of the pixels on upper and lower lines of the CCD 1 are added and mixed with each other and read. For example, in the case of the electric charges accumulated through the first-time exposure in a period of {fraction (1/60)} sec (vertical sync period), video signals in odd fields such as a mixed signal of lines 0 and 1, a mixed signal of lines 2 and 3, . . . are read as shown at the left side of FIG. 14. In the case of the electric charges accumulated through the second-time exposure in a period of {fraction (1/60)} sec, video signals in even fields such as a mixed signal of lines 1 and 2, a mixed signal of lines 3 and 4, . . . are read as shown at the right side of FIG. 14.
Therefore, a two-line mixed signal of the CCD 1 becomes a one-line signal of a field image and an odd-field signal and an even-field signal read by shifting one line are alternately output every exposure in a period of {fraction (1/60)} sec. These odd-field and even-field signals are interlaced and scanned to form a one-frame image and the one-frame image is displayed on a monitor as a dynamic or static image.
However, the above simultaneous electronic endoscope system has a problem that the quality (resolution or color shift) of, particularly, a static image is deteriorated if there is a time shift of {fraction (1/60)} sec between an odd-field signal and an even-field signal for forming a one-frame image and an endoscope or an object to be observed is moved during the time shift.
Therefore, the present applicant uses an every-pixel read mode for reading the data for every pixel obtained through one-time exposure immediately before by setting and using a predetermined shading period. However, by driving a shading shutter for setting the shading period, a mechanical (such as a gear) response delay occurs. That is, because a complete shading state is necessary for the shading period for reading data, the shading shutter is operated slightly before the shading period by considering the response time. In this case, the luminous energy for the exposure immediately before is reduced due to the then response operation (operation until complete shading is realized). Moreover, when adjusting the luminous energy emitted from a light source by a diaphragming mechanism, problems occur that the response time of the shading shutter changes depending on the opening state of the diaphragm and insufficient luminous energy changes.
FIG. 15 shows the relation between diaphragm member of a diaphragming mechanism and shading shutter for setting a shading period. For example, a diaphragm vane 3 and a shading shutter 4 are arranged so as to be able to shade a luminous flux (diaphragm opening) 100 from a light source. In this case, the diaphragm vane 3 is set so as to rotate about a rotary axis 3A and the shading shutter 4 is set so as to rotate about a rotary axis 4A clockwise. Moreover, the diaphragm vane 3 is driven so that the brightness signal of a video signal becomes constant. For example, by increasing luminous energy at a far point and reducing it at a near point, a preferable image can be obtained. Moreover, by rotating the shading shutter 4 one turn at a predetermined rotational speed, the shutter 4 is moved so as to completely shade the luminous flux 100 for a period of {fraction (1/60)} sec.
In the case of the above structure, however, because the diaphragm vane 3 and shading shutter 4 are rotated in the same direction, the timing for the shading shutter 4 to shade an actual luminous flux 100P depends on the driving position of the diaphragm vane 3 and the response time for completely shading the luminous flux 100P changes. That is, in FIG. 15, to completely shade the actual luminous flux 100P, the shading shutter 4 rotates by a rotational angle of xcex81 when the diaphragm vane 3 fully opens, by a rotational angle of xcex82 when the diaphragm vane 3 is present at the continuous line, and by a rotational angle of xcex83 when the diaphragm vane 3 is present at the two-dot chain line and resultantly, the response time is changed.
FIG. 16 shows the relation between luminous energy C (light quantity) of the luminous flux 100 and response time (luminous energy is assigned to vertical axis and time is assigned to horizontal axis). This diagram compares a case in which the diaphragm vane 3 fully opens and the response time ta1 when completely shading the luminous flux 100 is equal to 2 mS (sec) with a case in which the diaphragm vane 3 is present at a position for shading the half of a diaphragm opening 2 and the response time ta2 when shading the remaining half of the luminous flux 100 is equal to 1 mS.
In this case, when the diaphragm fully opens and the response time ta1 is equal to 2 mS, the electric charge quantity to be accumulated by the CCD 1 is normally shown by the following expression by assuming the luminous energy C for unit time when the diaphragm fully opens as 4 V and the exposure time (tb) as {fraction (1/60)} sec.
tbxc3x97C={fraction (1/60)}[mS]xc3x974[V]≢66.67 [mVs]
Moreover, the electric charge quantity when setting a shading period is obtained as shown below by assuming an attenuation line at the response time ta1 as a straight line.
tbxc3x97Cxe2x88x92(xc2xd)ta1xc3x97C={fraction (1/60)}[mS]xc3x974[V]xe2x88x92(xc2xd)xc2x72[mS]xc3x974[V]≢62.67[mVS]
Therefore, the luminous energy when setting a shading period is reduced to 94% of the normal luminous energy (luminous energy reduction of 6%) and also, the brightness of an image lowers by 6%.
However, when the diaphragm half opens and the response time ta2 is equal to 1 mS, the electric charge quantity accumulated by the CCD 1 is normally obtained as shown below by assuming the luminous energy C in this case as 2 V and the exposure time (tb) as {fraction (1/60)} sec.
tbxc3x97Cxe2x88x92{fraction (1/60)}[mS]xc3x972[V]≢33.33 [mVS]
Thus, the electric charge quantity when setting a shading period is obtained as shown below.
tbxc3x97Cxe2x88x92(xc2xd)ta2xc3x97C={fraction (1/60)}[mS]xc3x972[V]xe2x88x92(xc2xd)xc2x71[mS]xc3x972[V]≢32.33[mVS]
Therefore, the luminous energy when setting a shading period is reduced to 97% of the normal luminous energy (luminous energy reduction of 3%) and the brightness of an image also lowers by 3%.
Thus, when the response times ta1 and ta2 are different from each other, the rates of reduction of photographing luminous energy are different from each other, the luminous energy reduction increases as the response time ta increases, and resultantly the image brightness changes.
The present invention is made to solve the above problems and its object is to provide an electronic-endoscope light source unit for setting a shading period, capable of eliminating the fluctuation of luminous energy reduction so that the response time of a shading mechanism becomes constant by an electronic endoscope for reading every pixel by setting the shading period even when a diaphragm opening degree differs.
To achieve the above object, an electronic-endoscope light source unit of the present invention includes first shading means for shading a light-source luminous flux in a predetermined shading direction and second shading means for shading the light-source luminous flux in a shading direction almost perpendicular to the shading direction of the first shading means to set a shading period by using one of the first shading means and the second shading means as a diaphragming mechanism and the other shading means as a fully-closed shading mechanism for setting a fully-closed shading period for reading the signal of every pixel accumulated in an image pickup device.
In the case of the above structure, it is possible to arrange a shading mask having a quadrate opening, move the diaphragm member of the diaphragming mechanism along two sides of top and bottom or right and left of the quadrate opening, and move the shading shutter of the full-closed shading mechanism along other two sides.
It is possible to apply the above light source unit to an electronic endoscope system for reading the signal of every pixel accumulated in a solid-state image pickup device by using a shading period. In this case, an image-pickup-device driving circuit is able to execute an under-image-pickup-device-outputting pixel-mixing read mode for mixing video signals accumulated in an image pickup device between upper and lower lines and outputting them to form a dynamic image and an every-pixel read mode for reading the signal of every pixel accumulated in the image pickup device through one-time exposure by using the shading period to form a static image.
According to the above structure, a shading mask having a rectangular opening is set, a diaphragm member moves along the right and left sides of the shading-mask rectangular opening, and a shading shutter moves along the top and bottom sides perpendicular to the right and left sides. Therefore, even if a diaphragm member is set to any diaphragm position, the time for the shading shutter to shade a light-source luminous flux, that is, the response time of the shading shutter becomes almost constant. As a result, a luminous-energy deficiency caused by the response time (response delay) becomes constant and the fluctuation of luminous energy reduction under the exposure immediately before setting a shading period is eliminated.
Then, a high-quality static image is formed through, for example, the every-pixel read mode. In the every-pixel read processing, for electric charges accumulated through the exposure in a predetermined (assumed as first) period (vertical sync period) of {fraction (1/60)} sec, odd lines of an image pickup device are read in the second period ({fraction (1/60)} sec), remaining even lines are read in the third (next exposure) period, and these data values are stored in a predetermined memory. Moreover, the second period is set as a shading period so that the even lines can be read.
That is, when electric charges for the next exposure are accumulated in the second period for reading accumulated electric charges of the odd lines as ever, it is impossible to read remaining even lines. Therefore, accumulated electric charges of even lines are read in the third period by using the second period as a shading period. Thereby, it is possible to read the signal of every pixel of an image pickup device obtained through one-time exposure.
Then, video signals of odd lines and even lines stored in the memory are adjusted in phase and then, pixel mixing is performed between odd and even lines by a mixing circuit. That is, the pixel mixing forms a signal equivalent to the case of the under-image-pickup-device-outputting pixel-mixing read mode executed when a signal is output from an image pickup device. However, the signal is different from the case of the under-image-pickup-device-outputting pixel-mixing read mode in that pixel mixing is performed in accordance with the data obtained through one-time exposure.
When a dynamic image is normally displayed, the under-image-pickup-device-outputting pixel-mixing read mode is selected and pixels of two horizontal lines are mixed and read when output from an image pickup device as ever. Therefore, it is possible to obtain a dynamic image accurately reproducing the movement of an object through the image pickup with time.
Moreover, another invention has a shading member whose outer periphery is formed into the Archimedean spiral as the above second shading means to move the outer periphery of the shading member in the direction perpendicular to the shading direction of the above first shading means.
According to the above structure, by rotating the shading member of the second shading means, the shading member shades a circular luminous flux while the outer periphery of the Archimedean spiral almost linearly moves in a predetermined direction of the luminous flux. Moreover, when using the second shading means as a full-closed shading mechanism and the first shading means as a diaphragming mechanism, a shading shutter is set so that the outer periphery of the Archimedean spiral moves in a direction almost perpendicular to the rotational direction of a diaphragm vane. Thereby, even if the diaphragm vane moves to any diaphragm position, the shading shutter completely shades light-source luminous fluxes at almost the same time and the response time of the shading shutter becomes constant. As a result, the luminous energy deficiency caused by the response (response delay) time becomes constant and the fluctuation of the luminous-energy reduction at the time of the exposure immediately before setting a shading period is eliminated.
Still another invention is provided with a shading mask for controlling the passing range of a light-source luminous flux with an almost-V-shaped opening, a shading member for rotating about the V-shape intersection of the opening of the shading mask, first shading means for shading the V-shaped opening in accordance with the rotation of the shading member, and a shading member for moving in a direction almost perpendicular to the rotational direction of the first shading means, includes second shading means for shading the V-shaped opening by the shading member, and uses one of the first shading means and second shading means as a diaphragming mechanism and the other shading means to set a full-closed shading period for reading the signal of every pixel accumulated in an image pickup device. For example, it is possible to use the first shading means as a full-closed shading mechanism and the second shading means as a diaphragming mechanism. Moreover, it is possible to use means having a shading member whose outer periphery is formed like the Archimedean spiral as the first or second shading means.
Also, the present light source unit makes it possible to form a dynamic image in accordance with the under-image-pickup-device-outputting pixel-mixing read mode and form a static image in accordance with the every-pixel read mode.
According to the above structure, the rotation axis of the fan-shaped shading shutter of the full-closed shading mechanism is set to the V-shape intersection of the opening of the shading mask and the shading shutter rotates from one side toward the other side of the V shape of the opening. However, the diaphragm plate of the diaphragming mechanism linearly moves from the V-shaped-opening expanded side (upper side) toward the intersection. Thereby, even if the diaphragm plate moves to any diaphragm position, the shading shutter rotates by the V-shape opening angle whenever completely shading a light-source luminous flux and thereby, the luminous-flux shading time, that is, the response time of the shading shutter becomes constant. As a result, the luminous energy deficiency caused by the response (response delay) time becomes constant and the fluctuation of the luminous energy reduction under the exposure immediately before setting a shading period is eliminated.